After i updated to el Capitan, my 1680x1050 resolution-setting was gone!
So thank you very much for the updated steps, it is straight forward.
But one thing was getting me nuts in the process:
Please correct the path of the DisplayVendorID-610 folder. It's
(..)/System/Library/Display
s/Contents/Resources/Overrides/DisplayVendorID-610
As a terminal-n00b, i was getting desperate and searched for my spelling-fault and slash-fails for about an hour. (the
Macintosh\
HD placeholder didn't helped at all

)
The upside of the story: i learned some terminal commands and rules in this process